This invention relates to an electrolyzer comprising individual cells which are geometrically arranged one behind the other and consist each of two metallic partitions disposed between the cell and the adjacent cells, which partitions are provided with profiled spacing means on both sides, a diaphragm disposed between the partitions, and apertured electrodes which are mounted on both sides of and spaced from the diaphragm and are joined to and in contact with the profiled spacing means disposed on that side of the associated partition which faces the diaphragm.
Commercially offered electrolyzers comprise a plurality of individual cells, each of which comprises a pair of electrodes, each of which is separated from the adjacent cell by an embossed, preferably goffered, entirely nickel-plated, metallic sheet metal partition and which are separated by a platelike diaphragm. Said cells are electrically and geometrically arranged one behind the other. The partitions are inserted in an annular metallic frame. Each metallic partition is provided on its anode and cathode sides with an electrode consisting of a woven wire mesh of nickel-plated and activated steel or a woven wire mesh consisting entirely of nickel and said electrode is forced by the other electrode against the humps of the goffered partition. A diaphragm consisting of an asbestos plate has been inserted into the space that is defined between the electrodes. Each partition is bipolar because it carries a cathode on one side and an anode on the other side. The gases evolved at each electrode rise in the space between the electrode and the partition and are conducted away from there (Lurgi-Schnellinformation D 1073, November 1981 "Wasserstoff aus Wasser", self-published in Frankfurt, 1981).
That design of a cell has given rise to the suggestion to press electrodes provided with numerous outwardly flaring conical apertures onto both sides of the diaphragm because it was assumed that any decrease of the distance between the electrodes will reduce the internal cell resistance of the electrolyzer and will thus minimize the loss of energy involved in the transportation of the current between the electrodes (Winter Z. J. and J. Nitsch: Wasserstoff als Energietrager, Springer-Verlag Berlin-Heidelberg-New York-Tokio 1986, pages 180/181). A major part of the gases will be evolved only on the side that is remote from the diaphragm because the side which faces the diaphragm is electrically substantially insulated by a thin gas film between the diaphragm and the electrode and will not contribute to the production of gas. As a result, the lines of current flow extend through the apertures of the electrode to the rear side thereof. Owing to the number of apertures which are required for that purpose, the effective electrode surface area is reduced by 20 to 30%, the lines of current flow are unnecessarily long and the equalization of the concentration of the electrolyte consisting, e.g., of 25% potassium hydroxide solution in the diaphragm is restricted because the exchange of electrolyte is restrained. The energy loss may be so high that it will entirely compensate the energy gain that can be achieved because the electrodes are arranged without a clearance. Besides, the provision of electrodes arranged without a clearance usually involves the use of a diaphragm having a thickness of 0.2 mm not in excess of 0.5 mm and involves the risk of a local corrosion and/or an overheating resulting in a risk that the diaphragm may be destroyed so that the electrodes of a cell may be short-circuited. This may result in a melting of the metallic parts of the cell so that an entire series of cells may break down.
Such local short circuits may be initiated, inter alia, by small metallic particles, which have inadvertently been enclosed between and an electrode and a diaphragm and forced into the latter during the assembling of the cells. Small errors in the manufacture of the diaphragms and/or electrodes may also result in a local corrosion, in a destruction of the diaphragm, and in a short circuit between the electrodes.
French Patent Specification 2,460,341 discloses nets which consist of insulating material and are provided as spacers between electrodes and the metallic diaphragm to effect an electrical insulation as is called for by the object. Such nets will undesirably obstruct the flow of the mixture of electrolyte and gas bubbles and the exchange of electrolyte.
The problems described hereinbefore will also arise with cells in which the electrodes are spaced a comparatively very small distance of 0.1 to 0.2 mm from the diaphragm by so-called "microspacers", which are interposed. (International Journal of Hydrogen Energy, Vol. 13, No. 3, Pergamon Press, Oxford 1988, pages 148/149).
For this reason it is an object of the present invention so to design the electrolyzer cell which has been described hereinbefore that a high safety against short circuits and corrosion will be ensured and that the energy consumption will be as high as or lower than in a clearanceless electrode assembly.